The present invention relates to a combination weighing apparatus, and more particularly to a combination weighing apparatus which is provided with a control system to improve accuracy in combination processing.
There are known combination weighing apparatuses of two types I and II as described below.
Type I: The combination weighing apparatus of this type comprises a plurality of receptacle sets each consisting of one weighing bucket "WB" and one auxiliary bucket "MB", as shown in FIG. 15. The weighing bucket "WB" weighs a mass of material which is transported thereto and then transfers the weighed mass to the auxiliary bucket "MB", the weighed mas being temporarily held therein. Such masses of material which are weighed and contained in said weighing bucket and auxiliary bucket are subject ot selection which is made in combination processing to give a batch of predetermined weight. Selected weighing buckets "WB" and auxiliary buckets "MB" have to discharge their contents.
Type II: The combination weighing apparatus of this type comprises a plurality of receptacle sets each consisting of one weighing bucket "WB" and two auxiliary buckets "MB", as shown in FIG. 16. The weighing bucket "WB" weighs a mass of material which is transported thereto and then transfers the weighed mass to either auxiliary bucket "MB" which is selected, the weighed masses being temporarily held in the auxiliary buckets. Such masses of material which are weighed and contained in said auxiliary buckets are subject to selection which is made in combination processing to give a batch of predetermined weight. Selected auxiliary buckets "MB" have to discharge their contents.
FIGS. 17a and 17b respectively illustrate two possible modes of operation in the known combination weighing apparatuses described above. In one of the operation modes shown in FIG. 17a, a mass of material which was previously weighed by the weighing bucket "WB" and transported therefrom to either auxiliary bucket "MB" so as to be temporarily stored therein will be discharged therefrom at a time when a command is given to the auxiliary bucket as a result of combination processing, after the mass has become stable in said auxiliary bucket. In the other operation mode shown in FIG. 17b, such a command to discharge a mass of material stored temporarily in the auxiliary bucket "MB" is given thereto as a result of the combination processing, before said mass has not completely been transferred to said auxiliary bucket. The outlet gate of the weighing bucket "WB" is opened to transfer the contents thereof to the auxiliary bucket "MB" in such a manner as illustrated in FIGS. 17a and 17b. The outlet gate of the auxiliary bucket "MB" is also opened to discharge its content in a manner as illustrated in said FIGS. 17a and 17b, reference symbols "T.sub.x " and "T.sub.y " (T.sub.x &lt;T.sub.y) written thereon respectively denoting periods of time during which the outlet gates of the weighing bucket and auxiliary bucket are kept open to transfer or discharge their contents.
It will be apparent that in the prior art the known apparatuses need the period of time "T.sub.y " was lengthened to excess in order to completely discharge the weighed and temporarily stored mass without failure in any cases because there was a high probability that said mass would be discharged by the combination processing before it has been completely transferred to the auxiliary bucket "MB".
Such an excessively long period of time employed for the purpose of safety is, of course, apt to prolong each weighing cycle time "T.sub.o " which consists of the following periods of time "T.sub.a ", "T.sub.b ", "T.sub.c " and "T.sub.d ".
The period of time "T.sub.a " is the calculation period needed to select the masses of materials during the above-mentioned combination processing. The other period of time "T.sub.b " (="T.sub.y ") is the discharging period during which the outlet gate of the auxiliary bucket "MB" remains open for discharging its content. The further period of time "T.sub.c " is the transferring period during which the outlet gate of the weighing bucket "WB" remains open to transfer the mass of material therefrom to the auxiliary bucket "MB". The still further period of time "T.sub.d " is the stabilizing period during which the mass of material is charged into the weighing bucket "WB" and subsequently the state of said mass becomes stable therein.
Comparison of FIG. 17a with FIG. 17b will make more apparent the abovedescribed problem. The period "T.sub.x " will suffice as such discharging period "T.sub.b " for keeping open the auxiliary bucket's outlet gate in the case shown in FIG. 17a, but instead, a longer period "T.sub.y " shown in FIG. 17b will be employed therefor in the known apparatuses. This results in the weighing cycle time "T.sub.o " which is unnecessarily made long so that the number of weighed masses of material which can be selected in the combination processing will inevitably decrease as a whole, thereby making it difficult to improve the accuracy and efficiency of the combination processing.